1. Technical Field
The present disclosure relates to a common mode choke coil, and particularly relates to a common mode choke coil having three windings.
2. Description of the Related Art
The wound-type common mode choke coil disclosed in Japanese Patent No. 3952971 is known as an example of a conventional common mode choke coil. This common mode choke coil is configured with three wires wound around a core so as to form three coils (a first coil to a third coil). FIG. 9 is a circuit diagram illustrating a transmission/reception system in which a wound-type common mode choke coil 110 disclosed in Japanese Patent No. 3952971 is applied.
As illustrated in FIG. 9, the common mode choke coil 110 is provided between a transmission circuit 120 and a reception circuit 122. Specifically, a first coil 112 is connected partway along a signal line 123 that connects the transmission circuit 120 and the reception circuit 122, a second coil 114 is connected partway along a signal line 124 that connects the transmission circuit 120 and the reception circuit 122, and a third coil 116 is connected partway along a ground line 126 that connects the transmission circuit 120 and the reception circuit 122.
In this transmission/reception system, transmission signals Sig1 and Sig2 are transmitted from the transmission circuit 120 to the reception circuit 122 through the signal lines 123 and 124, respectively. In this case, the transmission signals Sig1 and Sig2 are transmitted from the reception circuit 122 to the transmission circuit 120 through the ground line 126. As a result, the orientation of a magnetic field generated by the first coil 112 and the orientation of a magnetic field generated by the second coil 114 are opposite to the orientation of a magnetic field generated by the third coil 116. In other words, the magnetic fields generated by the first coil 112 and the second coil 114 and the magnetic field generated by the third coil 116 cancel each other out. As a result, a magnetic flux density in the core is suppressed from becoming too high, and magnetic saturation is suppressed. In other words, the common mode choke coil disclosed in Japanese Patent No. 3952971 has excellent DC superposition characteristics.
However, according to the common mode choke coil disclosed in Japanese Patent No. 3952971, it is difficult to increase a rated current value. More specifically, a larger current flows in the third coil 116 than in the first coil 112 and the second coil 114. The first coil 112, the second coil 114, and the third coil 116 have the same number of turns, and thus the first coil 112, the second coil 114, and the third coil 116 have the same resistance value. Accordingly, the third coil 116 is more prone to emitting heat than the first coil 112 and the second coil 114. For this reason, the rated current value of the common mode choke coil is determined by an upper limit value of the current that can be flowed through the third coil 116. As a result, even if a current that is smaller than the rated current value is flowing in the first coil 112 and the second coil 114, when a current equal to the rated current value flows in the third coil 116, a larger current than the presently flowing current cannot be flowed through the first coil 112 and the second coil 114. In other words, according to the common mode choke coil disclosed in Japanese Patent No. 3952971, it is difficult to increase the rated current value.